This application claims priority to German Patent Application No. 10045258.2, filed Sep. 12, 2000.
The invention concerns a roller cage for a minimum of one work roller of a tool for deep rolling of grooves or radii of crankshaft bearings, where the work roller is loosely guided at a section of its circumference, either by the roller cage or in a concave recess of the roller cage.
A prior art deep rolling tool is described in European Patent Application EP 0 839 607 A1. Deep rolling work rollers typically are loosely guided in roller cages identified by reference number 15. The roller cages are attached to the external end of the long leg of an L-shaped tool holder.
The deep rolling work rollers are described in U.S. Pat. No. 5,806,184. The work rollers are guided in roller cages. Work rollers for the deep rolling of grooves or radii of crankshaft bearings are highly stressed tools. Their wear and tear occurs, for example, by material chipping similar to that experienced in gears or in rolling elements of rolling bearings.
In a deep rolling tool known in the art, the work roller is vertically supported from above by one guide roller each. The total load applied to the work roller is generated by the contacts between thy work roller, the guide roller, the crankshaft and the roller cage. Of the two roller cages, each located opposite one work roller, only the one located in the crankshaft drive direction is subject to wear. A generally known practice for reduction of this wear and tear is to offset the work roller by a small amount, relative to a line formed by the crankshaft axis and the guide roller.
Work rollers are, however, not only stressed by pressure, but there is also slippage between the work roller, the crankshaft and the guide roller, since their effective radii roll off differently. The roller cage transfers the so generated rolling force directly to the work roller and is, for this reason, severely stressed by the slipping action, and wears fast accordingly. Previously this type of wear has been counteracted by applying oil lubrication or oil-air-lubrication using rolling oil, to the deep rolling tools. For oil lubrication a thin-bodied oil (5 CST) is used feeding very generous amounts.
The object of the invention calls for a reduction of wear for the roller cage. The means used for this purpose,should be easy to handle, reliable in operation, and also reasonably priced.
The object of the invention is attained in that at least those portions of the roller cage, or those sections of the concave recess at which, or in which, the work roller is guided in the roller cage, consist of a material that dispenses solid lubricant to the work roller. One suitable material of this type is, for example, graphite. A block of graphite is placed in a void of the roller cage and, during deep rolling, dispenses graphite particles to the work roller to provide lubrication.
Wear and tear of the graphite-holding portion of the roller cage is controlled in a simple manner by dimensioning the remaining portions of the roller cage not containing graphite, small enough to allow at all times a sufficiently large graphite layer to be removed along with their wear. These relationships are determined from case to case experimentally.
Materials other than graphite may also be utilized as a solid lubricant, such as MOS2. Also, the application of a sintered metal material for the roller cage may be considered. The porosity of the sintered metal material supports the application of a lubricant under external pressure. The lubricant passes through the sintered metal material and exits at places where the roller cage is in contact with the work roller.